The pressent invention relates to vane compressors for use, for example, as refrigerant compressors for air conditioning systems of vehicles.
In general, a vane compressor of the kind referred to above comprises a cam ring which has an inner peripheral surface formed into a camming surface and which has opposite axial ends closed by respective side blocks. A rotor is rotatably arranged within the cam ring. The rotor is formed therein with a plurality of axial slits in which vanes are slidably fitted respectively. The side blocks, the cam ring, the rotor and the vanes cooperate with each other to define a plurality of pumping chambers whose respective volumes vary with rotation of the rotor to compress fluid supplied into the pumping chambers.
In the vane compressor arranged as described above, the inner peripheral camming surface of the cam ring has a cam profile which has conventionally been determined based on a curve represented by the expression sin.sup.2 .theta. or the like, as disclosed, e.g. in Japanese Provisional Patent Publication (Kokai) No. 60-11601. In the conventional vane compressor comprising the cam ring formed with the inner peripheral camming surface having such cam profile, the tip of each vane is separated or disengaged from the inner peripheral camming surface of the cam ring at a location immediately behind each of regularly circular portions of the inner peripheral camming surface, with reference to the direction of rotational movement of the vane. The regularly circular portions are minor diameter portions where the outer peripheral surface of the rotor is in close contact with the inner peripheral camming surface. Because of such separation or disengagement of the vane tip from the inner peripheral camming surface, chattering of each vane tends to occur, resulting in an increase in fluctuation in torque of the rotor. A cause for such chattering is that the cam profile of the camming surface is designed such that an increasing rate in the amount of protrusion of each vane becomes high abruptly at the location on the inner peripheral camming surface immediately behind each of the regularly circular portions thereof, so that each vane cannot follow the designed increase in the amount of protrusion. If the cam profile of the camming surface is so designed that the increasing rate in the amount of protrusion at the location immediately behind each regularly circular portion is reduced in an attempt to enable each vane to follow the increase in the amount of protrusion, the maximum volume of each pumping chamber is reduced, resulting in a decrease in delivery quantity of the compressor.